1. Field of the Invention
The present invention generally relates to the control of SCR-type switches. The term “SCR-type switches” is here used to designate components such as thyristors, triacs, and controlled bidirectional switches of various types comprising four or five alternated semiconductor layers. The present invention especially applies to the case where the switches are medium-power switches intended to switch loads connected to the A.C. supply network (at 50 or 60 Hz).
2. Discussion of the Related Art
Generally, in the control of multiple switches and/or of switches supplied by the A.C. network, the problem of the isolation between the control circuit and the switch(es) to be controlled is posed, and a galvanic isolation circuit such as a transformer or an optocoupler is generally provided, which has the disadvantage of being expensive and difficult to integrate.
It has been provided, for example, in PCT patent application WO/0250850 which is incorporated herein by reference, to control power switches with high-frequency signals. In this patent application, the high frequency is used for the advantage that it has of enabling use of a small transformer, which enables galvanic isolation at lesser cost but however requires a transformer. After transformation, this high frequency is applied to the gate of the component to be switched via a rectifying diode, that is, in fact, the control is performed by signals in the form of D.C. pulses.